The present invention generally relates to systems and methods for quickly shrinking encasing materials.
To an ever increasing degree, fiber optic cabling and technology is being implemented in telephone, computer, and other networks. Additionally, fiber optic technology is increasingly being implemented at the device level, e.g., within computer devices and components. As a result, demand for fiber optic technology continues to increase. With this demand, comes a strong need to produce or prepare (i.e., process) fiber optic cables quickly and in high volume. A typical fiber optic cable includes an optical fiber strand encased by a protective sleeve or coating. Preparation of such a cable can include splicing strands together, which requires stripping the protective sleeve of coating from the strand. In such a case, once spliced, the spliced region of the strand requires protection, such as with a heat shrinkable sleeve.
The sleeve may be comprised of any of a variety of optically opaque materials that can be shrunk onto the fiber strand. Such sleeves are usually made out of some form of shrinkable polymer and are made to be of a diameter sufficiently large so that the fiber strand can be easily slipped (or loaded) into the sleeve, referred to as a xe2x80x9cloaded sleevexe2x80x9d.
With current technology, a loaded sleeve is positioned in a fixed relatively cool convection oven. Such ovens typically require an operator to position the loaded sleeve in the oven for heating and shrinking, so the oven is returned to a relatively cool temperature to lower the risk of heat related injury or damage. Once the loaded sleeve is in the oven, and the oven is closed, the oven is turned. After about sixty (60) to ninety (90) seconds the oven heats up to the temperature required to shrink the sleeve onto the strand (i.e., a target heat shrink temperature). A typical heat shrink temperature is about a minimum of 90xc2x0 C. to about 240xc2x0 C., depending on the sleeve.
The time it takes for the oven to achieve its target heat shrink temperature is referred to as the temperature ramp-up time. When the oven reaches the heat shrink temperature, the sleeve begins the process of shrinking around the fiber strand. Once the loaded sleeve has been in the oven and heated at the heat shrink temperature for an adequate amount of time, the sleeve is shrunk to snuggly encase the strand. The loaded sleeve is then removed from the oven and placed in a cool down area. Again, this is performed by the operator. Meanwhile, the oven also cools down. Later, it is reheated to process another loaded sleeve.
As a result, current technology requires a heat shrink cycle time of approximately sixty (60) to ninety (90) seconds from start to finish to shrink a sleeve around a fiber strand, depending on the characteristics of the sleeve (e.g., diameter, thickness, and composition), the heat shrink temperature, the oven""s temperature ramp-up time, and the speed of the operator.
One problem with the current approach is that the processing of fiber optic cables is limited by the relatively long heat shrink cycle time. Additionally, the typical approach does not economically lend itself to automation, which might offer some reduction in the heat shrink cycle time.
As a result, among other things, it is an object of the present invention to reduce the heat shrink cycle time of fiber optic cable processing, and thereby facilitate larger volumes of fiber optic cable processing in shorter amounts of time. It is another object of the present invention, to apply these same benefits in other than fiber optic processing, where shrinkable sleeves or encasings are useful.
The present invention provides a system and method for quickly heating a shrinkable casing around a relatively non-shrinkable object. The system may be referred to as a sleeve shrinking quick dip heat system. As one example, the present invention may be used to shrink a sleeve around an optical fiber strand. In the electrical and electronic fields, the present invention may be used to shrink sleeves or tubing around, for example, copper strands, wires, connectors, or components. Collectively, these strands, wires, connectors, devices, and components are referred to as xe2x80x9cstrandsxe2x80x9d. In the fiber optic field, sleeves are typically made of some form of optically opaque polymer, known in the art. This same type of material can also be used in the electrical or electronic fields. For example, those skilled in the art will appreciate that the present invention may be used with typical heat shrinkable dual wall sleeves and tubing. Collectively, the heat shrinkable materials, casings, sleeves, and tubing are referred to as xe2x80x9csleevesxe2x80x9d.
In accordance with the present invention, a heater assembly is provided that includes a loaded sleeve holder, a heating block and a heater element, encased in a heating chamber. In order to shrink sleeves around a fiber strand, as an example, the strand is loaded into a sleeve, such that the sleeve loosely encases the strand. The loaded sleeve is positioned in the loaded sleeve holder for shrinking. The heater block, which is thermally coupled to the heater element, is brought into contact with the sleeve holder, which maybe in the form of a channel that supports the loaded sleeve. In one form, the heater block is movable, so it is moved to contact the sleeve holder. In another form, the sleeve holder is movable, and moved to contact the heater block. In yet another form, the heater block and sleeve holder may each be movable, so they move together until contact.
In typical heat shrinkable sleeves, heat shrink temperatures range from about 90xc2x0 C. to 240xc2x0 C., depending on the physical and thermal parameters of the sleeve. It is, of course, presumed that the strand is capable of withstanding the heat shrink temperature and duration required to shrink the sleeve. In the present invention, the heater block is maintained at the heat shrink temperature for successive shrinking operations, without the requirement of temperature ramp-up for each heat shrinking operation. Other temperatures and ranges can also be accommodated, depending on the characteristics of the sleeves.
The heater block is formed from a material that is highly thermally conductive, such as to aluminum. The heater block is thermally coupled to the heating element (or cartridge), and preferably maintained at or near the heat shrink temperature of the sleeve being shrunk. A heat sensor may be included to monitor the temperature of the heater block. Unlike a convection oven, the temperature inside the heating chamber need not achieve the heat shrink temperature, since the present invention uses local (e.g., contact) heating. That is, in one form, the heater block is made to contact the sleeve holder. The heat is transferred to the sleeve holder, according to the temperature profile of the sleeve holder, and the sleeve holder then transfers the heat to the sleeve for shrinking. In one form, once a door to the heating chamber is closed, the heating block moves to meet the stationary sleeve holder for heating, and then retracts once heating is accomplished. A user interface is provided with the chamber to adjust and monitor the temperature of the heating block, as well as to control the movement of the heater block and/or sleeve holder.
In order to maintain the loaded sleeve in position for shrinking, the stand holder includes a channel within which the loaded sleeve is placed. The sleeve holder is preferably made from a material having a low thermal mass and a high thermal conductivity, such as aluminum, steel, or copper (as examples). As a result, the sleeve holder heats up and cools down quickly. The sleeve holder is heated when placed in contact with the already heated heater block, so high thermal conductivity allows the sleeve holder to heat quickly, saving time. The low thermal mass allows the sleeve holder to cool quickly, making it safe.
The heater block includes a sleeve holder engager. The sleeve holder engager and/or the sleeve holder are configured to achieve a predetermined temperature profile. If sleeves are shrunk such that the center and ends are shrunk at the same time there is a chance that air bubbles will be trapped inside the sleeve, which can degrade the performance characteristics of the cable. Accordingly, in one form of the present invention, a high yield heat shrinking process is obtained by shrinking the sleeve from the center toward its ends. This approach forces the air out of both ends of the sleeve as the sleeve shrinks from the center outward. In such a case, the sleeve holder engager and/or sleeve holder are configured such that the shrink temperature transferred to the center of the loaded sleeve is slightly higher than at the loaded sleeve""s ends, so the sleeve shrinks more quickly at its center.
This can be accomplished in a variety of manners. In a first manner, a decreasing amount of contact is provided between the sleeve holder and the ends of the loaded sleeve. Heat sinking the ends of the sleeve holder provides another approach to keeping the ends cooler than the center of the sleeve holder. In another form, a decreasing amount of contact between the heater block and the ends of the sleeve holder (e.g., the sleeve holder can be made to be longer than the heater block. In another form, the composition of the sleeve holder is such that the thermal connectivity at the center is greater than it is at its ends. In yet another form, a thermal resistance within the cross section of the of the sleeve loader is such that there is a xe2x80x9ctime lagxe2x80x9d before the ends reach the heat shrink temperature. Such thermal resistance can be achieved by providing holes in the sleeve loader between its center and its ends. In any of these various approaches, a thermal gradient is provided between the center and ends of the sleeve holder, with the highest temperatures at the center, at least initially.
In another form of the present invention, a high yield heat shrinking process may be obtained by shrinking the sleeve from one end to the other end. In such cases, the temperature applied to a loaded sleeve at a first end is greater than it is a second, opposite end. According to this approach, air is forced out of the second end of the sleeve as the sleeve shrinks from the first end. Such temperature gradients may be formed in any of a variety of manners, as discussed above.